This invention relates to techniques for contacting sensor microstructures.
There has now been developed a wide range of microelectromechanical systems, including microsensors and microactuators, for sensing, measurement, and movement in the micron regime, i.e., in the dimensional range of microns. Such microelectromechanical systems have been shown effective and efficient at sensing and measuring stress, temperature, pressure, and flow rate, for example, among other characteristics, as well as performing micromovement actuation in response to sensed or imposed stimulation. The success of microelectromechanical systems has in part been due to the ability to produce them using conventional microfabrication techniques with conventional electronic materials, exploiting the mechanical properties of these electronic materials. Silicon in particular has been shown to have excellent mechanical properties and lends itself well to microstructure fabrication.
In a typical microsensor application, the sensor is preferably located in intimate, unobstructed contact with the environment to be sensed, and yet should not, by the nature of its presence in that environment, alter or inhibit characteristics of the environment. This places difficult constraints and requirements on sensor packaging the contact design. For example, in a flow sensor, it is imperative that any electrical, mechanical, or other contact to the sensor not form a protrusion, even on the micron scale, into the stream of flow to be measured which could perturb the flow characteristics of the system in the vicinity of the sensor; such perturbation would obviously impact the clarity and trueness of flow measurements.
Furthermore, many industrial manufacturing processes, e.g., melt extrusion, have historically evolved to permit on-line measurement of manufacturing characteristics only in a manner that inherently does not disturb the manufacturing process while monitoring it. Thus the successful application of microelectromechanical sensors to manufacturing processes as substitutes for conventional macro-sized sensors that have historically provided such monitoring requires that the microsensors have the same non-intrusive characteristics as the macro-sized sensors; and indeed, it has been shown that a given microsensor is inherently capable of being less intrusive and at the same time more effective than its macro-sized counterpart.
To complicate matters further, operation of typical microelectromechanical sensors is based on some type of moveable microstructure whose motion is correlated to an attribute of interest to be sensed and measured. Exposure of the microstructure to the process to be monitored should not perturb the process environment as the microstructure moves in the environment, and furthermore, packaging of and contact to the microstructure should not perturb the process environment. In monitoring an extrusion process, for example, a melt monitoring sensor such as a shear stress sensor, positioned in a wall of the melt extrusion barrel, should not perturb the flow of melt through the extruder barrel and yet must intimately contact the flowing melt. As a result, complicated and elaborate electrical power and read out connections for flow sensors have typically been used to avoid perturbing the flowing melt to be sensed.
In one such microelectromechanical shear stress sensor, designed for measuring shear stress of a flowing fluid such as an extruded melt, disclosed in U.S. Pat. No. 5,199,298, by Ng et al., issued Apr. 6, 1993, an electrical contact strip layer is located on the top face of a movable, floating element which measures shear stress of the melt, fully exposed to the melt fluid being monitored. The contact strip layer thus protrudes into the melt stream, affecting the stream flow, and depending on its material, possibly introducing unwanted constituents into the melt or itself being impacted by the melt constituents. In an alternative embodiment of U.S. Pat. No. 5,199,298, it is suggested that some type of contact to the floating element could be formed through the wafer on which the floating element is fabricated, near to the end of the floating element fabrication sequence, after the floating element has been fabricated. This contact scheme is intimately tied to the particular preferred floating element geometry of U.S. Pat. No. 5,199,298, and so is not readily applicable to other sensor designs. For example, the common situation in which isolated electrical contact must be made to adjacent sensor or wafer regions is not addressed by the geometry of U.S. Pat. No. 5,199,298; no lateral isolation of contact points is provided for with that structure.
Other proposed sensor microstructure contact schemes have also been tied to a particular sensing structure, and due to this, as well as fabrication complexity, are likewise not generally applicable to microstructure designs. Perhaps most importantly, such schemes typically provide for only one mode of contact, for example, fluid contact, without providing for other modes of contact, such as mechanical. Thus, to this time, an adaptable, generally applicable, non-intrusive sensor microstructure contact scheme is yet to be attained.